Sound producing device



Jam. 3, 1933. c. M. BOUDETTE 1,893,049

SOUND PRODUCING DEVICE.

Filed Aug. 30, 1932 2 Sheets-Sheet l Jan. 3 W33 c. M. BOUDETTE 178937949SOUND PRODUCING DEVICE Filed Aug. 30, 1952 2 Sheets-Sheet 2 lllllll \w IINVENTUR: I

Patented Jan. 3, I933 PTENT' UFFICE CLAYTON MI. BOUDETTE, F REVERE,MASSACHUSETTS SOUND PRODUCING: DEVICE Application filed. August 30,1932. Serial No. 631,039.

In radio loud speakers of the electrodynamic type where thevoice-current coil is disposed in the air gap between the core andpole-piece of a magnet, usually an electromagnet, it is desirable toreduce the radial length of such air gap to a minimum and it isessential that said diaphragm and the actuating coil attached thereto beaccurately centered with respect to said core so that said coil 19 mayhave free and unrestricted longitudinal movement, and no transversemotion, in said gap.

This invention involves a novel coil-supporting means which, whilepermitting free 35 longitudinal movement of the voice current coil inthe air gap, accurately centers said coil and prevents any transversemovement thereof, thereby eliminating all danger of contact between saidcoil and the magnet ele- 29 ments. By means of this improved centeringdevice a much narrower air gap can be used than is possible with thecoil-centering means heretofore employed and the diaphragm and voicecoil are permanently and accurately centered and aligned with respect tothe magnetic system.

The preferred form of centering device is a washer of thin flexiblenon-hydroscopic material such as celluloid, qmetal, bakelite, non- 30porous paper and the like which may be provided with corrugations,either concentric or spiral, or of any other suitable configuration toincrease the flexibility thereof longitudinally without unduly reducingthe lateral stiffness of the same. The voice-coil supporting-cylinderpreferably projects through the central aperture of the centering washerand is cemented to the latter and the apex portion of the diaphragm, ifthe latter be of the conical type, with the result that the washer actsas a diaphragm-supporting means, as well as a means for centering andaligning the voice coil and diaphragm with respect to the magneticstructure.

In the drawings which accompany and form a part of this specification-Figure 1 is a plan view of a coil-centering washer embodying the presentinvention;

Fig. 2 is a section taken on the line 22 of Fig. 1;

Fig. 3 is a plan view of another form of centering washer;

Fig. 4 is a section taken on the line 4-4 of Fig. 2;

Fig. 5 is a longitudinal central section of a radio loud speakerprovided with the coilcentering diaphragm-supporting washer shown inFig. 1.

In the particular drawings selected for more fully disclosing theprinciple of my invention and which are to be considered as illustrativemerely and not as restrictive, 10 is a washer formed of thin flexiblenon-porous material, such for example, as celluloid and provided withconcentric corrugations 11 between the peripheral portion 12 and the central aperture 13. The corrugated portion of the apertured disc or washerbetween the support for the peripheral portion thereof and said centralaperture must have such radial to length as will permit of sufficientlongitudinal movement of said disc and the parts thereto attached toeffect the faithful reproduction of low notes. In the present instance,as shown in the accompanying drawings which are full size, except thatthe thickness of the washer is greatly exaggerated for clearness ofillustration, the ratio of the diameter of the free or vibrating portionof the disc, i. e., the portion thereof within the inner periphery ofsaid support, to the diameter of said central aperture is 2% to 1,approximately, and the ratio of the radial length of the corrugatedportion of said disc to the thickness of the disc is approximately 250to 1. I do not, 55 however, limit myself to such ratios, the requirementbeing that the amplitude of range of vibration of the disc must berelatively large if low notes are to be reproduced with fidelity. By theloud speaker shown in the drawings, the lowest notes of the musicalscale are reproduced faithfully because a range of vibration of 4 inchcan be obtained without breaking or cracking the disc. It will beunderstood of course that I do not limit my- 95 self to a loud speakerof the exact size shown in the drawings and that the principleunderlying the speaker herein specifically disclosed is applicable tospeakers larger and smaller than the one illustrated in the drawings. 1W

I am aware that diaphragms with corruated peripheral portions have beenproposed or loud speakers of the horn type, but in such case the radiallength of the corrugated 5 portion thereof must be small compared to thediameter of the diaphragm to ensure the lateral stiffness necessary forpreventing the rocking of the diaphragm, with the result that thevibration range of such diaphra ms is much too small for the faithfulreproduction of low notes if said diaphragm were used in a speaker ofthe cone type.

Inasumch as the corrugation of a coil-centering disc reduces the lateralstifl'ness thereof and as such disc must have sufficient lateralstiffness to permit the use of an extremely narrow air gap, it followsthat the radial length of the corrugated portion of the disc mustnecessarily be a compromise between Such radial length must besufficiently great toimpart to the disc such elasticity as will permit,other things being equal, of a relatively large vibratlon range, and yetnot so great as to reduce the lateral stiflness of the disc to thedegree that will prevent the use of a narrow air gap with very smallclearance between the voice coil and the side of said g It will beobvious that if a voice coil of larger diameter than that shown in thedrawings is used, the ratio above-mentioned would be smaller than 2% to1.

It will be obvious also that the radial length of the corrugated portionof the disc, for a. given range of vibration, is dependent, other thingsbeing equal, upon the thickness of the disc, and further, that suchradial length for a given range of vibration and given thickness of discis dependent upon the size and. weight of the cone. For; example, if thethickness of the disc be reduced, the radial length of the corrugatedportion thereof also may be diminished, and if the size or weight of thecone be augmented, such radial length may be reduced, and vice versa.

In view of the various factors entering into the determination of theradial length of the corrugated portion of the washer or disc, it is tobe understood that I do not limit myself to any particular ratio ofdiameter of the free portion of the discto diameter of the centralaperture thereof, or to any particular ratio of radial length tothickness of disc, and that 55 I desire to cover by the appended claimsa loud speaker of the cone type in which the radial length ofthe-corrugated portion of the centering disc is sufiiciently great topermit of the range of vibration required, other 60 things being equal,for the faithful reproduction of low notes without sacrificing thelateral stiffness necessary to permit the use of an extremely narrow airgap. If celluloid is employed for the washer, the corrugationsconveniently may be formed by heating the longitudinal flexibility andlateral stiflness.

disc and pressing the corrugations thereinto by a die.

In Fig. 3 the disc is provided with concentric corrugations 14. It willbe understood that as the purpose of the corrugations is to increase theflexibility of the washer longitudinally without unduly reducing thelateral stiffness thereof, such corrugations may be of any sha e orconfiguration that will effect the desi 'result.

Referring to Fig. 5, the electromagnet 15 is provided with a core 16 andpole-piece 17, apertured to receive said core. The voicecurrent coil 18is wound on the coil-supporting cylinder 19 and is disposed in the airgap between the core and pole-piece. The outer flange 20 of thediaphragm 21, herein shown as a cone, is flexibly supported by theflange 22 of the pan 23 secured to the magnet structure by bolts 24. Thelower portion of said pan forms an annular support 25 for the outerperipheral portion of the centering washer which preferably is cementedto said annular support. Preferably a thin coating of cement is placedon the coil-supporting cylinder and the latter is then passed throughthe apex portion of the cone in order to secure these two elementstogether. The central aperture of the centering washer may be providedw1th a flange 26 inorder to facilitate the cementmg of said washer tothe coil-supporting cylinder, which preferably is secured both to thediaphragm and washer. It will be understood of course that thisinvention is not limited to the particular means disclosed for securingthe aforesaid elements together, inasmuch as many alternative means willreadily occur to those skilled in the art for accomplishing thispurpose.

It has been found'in practice that the use of a centering washer of thecharacter described herein permits the permanent and accurate centeringand aligning of the diaphragm and voice coil with respect to the magnetstructure and makes possible a substantial reduction in the radiallength of the air gap. The flexibility of the centering washer eflectedby the corrugations is such that the voice coil has free and unimpededmovement longitudinally with respect to the air gap while lateralstiffness thereof is not reduced sufficiently to permit any transversemovement of said coil in said gap.

It will be obvious that various changes in structure and relationshipmay be made by those skilled in the art without departing from the scopeof the invention as defined by the appended claims.-

I claim:'

1. A sound-producing device comprising in combination, a cone diaphragmflexibly supported at its base, an actuating coil secured to saiddiaphragm, a corrugated imperforate coil-centering diaphragm-supportingllt) thereof without unduly reducing the lateral stiffness of the same.

3. A sound-producing device comprising in combination, a cone diaphragmflexibly supported at its base, an actuating coil secured to saiddiaphragm, a coil-centering diaphragm-supporting disc of thin flexiblema- Lerial provided with concentric corrugations and a support for theperipheral portion of said disc, the corrugated portion of said dischaving-sufficient radial length to permit of free longitudinal movementthereof withou unduly reducing the lateral stifl'ness of the same.

4. A sound-producing device com rising in combination, a cone diaphragmexibly supported at its base, an actuating coil secured to saiddiaphragm, a coil-centering diaphragm-supportlng disc of thin flexiblematerial provided with spiral corrugations, and. a support for theperipheral ortionof said disc, the corrugated portion 0 said disc havingsufficient radial length to permit of free longitudinal movement thereofwithout unduly reducing the lateral stiffness of the same.

5. In a sound-producing device having a diaphragm flexibly supported atits base and an actuating coil secured thereto, a corrugated imperforatecoil-centering diaphra supporting disc of thin flexible non-hydi' scopicmaterial, and a support for the peripheral portion of said disc, thecorrugated ment thereof without unduly reducing the lateral stiflness ofthe same.

' 7. A sound-producing device com rising in combination, a conediaphragm flexibly supported at its base, a magnet having a core and apole-piece, a coil support, an actuating coil carried by said support,said coii bein disposed in the air gap pole-piece and c said core an ortbeing se cured to said diaphragm, a thin corrugated disc for centeringsaid coil, said disc being of thin flexible material and having acentral aperture for receiving said coil support, and a support for theperipheral ortion of said disc, the corrugated portion 0 said dischaving suflicient radial length to permit of free longitudinal movementthereof without unduly reducing the lateral stiffness of the same.

8. A sound-producing device com rising in combination, a cone diaphragmexibly supported at its base, a coil support, an actuating coil carriedby said support, a corrugated coil-centering disc formed of thinflexible material and provided with a central aperture, a support forthe outer peripheral portion of said disc, said coil support passmgthrough said aperture and being secured to said diaphragm and to saiddisc, and a magnet having a core and a pole-piece, said coil beingdisposed in the air-gap between said core and pole-piece and thecorrugated portion of said disc having sufiicient radial length topermit of free longitudinal movement thereof without unduly reducing thelateral stiffness of the same.

In testimony whereof I aflix my signature.

CLAYTON M. BOUDETTE.

